1. Field of the Invention
The present invention relates to a liquid crystal display device. The invention particularly relates to a liquid crystal display device taking measures to prevent bright spots caused by scraped dusts of an alignment film.
2. Description of the Related Art
Liquid crystal display devices include: a TFT substrate having pixel electrodes, thin film transistors (TFT), etc. formed in a matrix; a counter substrate disposed in facing relation to the TFT substrate and having color filters, etc. formed at positions corresponding to the pixel electrodes of the TFT substrate; and liquid crystals put between the TFT substrate and the counter substrate. Images are formed by controlling the light transmittance of liquid crystal molecules for each pixel.
In the liquid crystal display device, an alignment film is formed at the boundary between the counter substrate and the liquid crystal layer in the TFT substrate, and the alignment film is subject to rubbing process or optical alignment process to put the liquid crystal molecules to initial alignment. Then, the amount of light transmitted through the liquid crystal layer is controlled by twisting or rotating the liquid crystal molecules by electric fields from the state of initial alignment.
Meanwhile, to control the thickness of the liquid crystal layer, it is necessary to form spacers between the counter substrate and the TFT substrate. Conventionally, beads, etc. were dispersed as the spacers in the liquid crystal layer. In recent years, however, to control the gap between the TFT substrate and the counter substrate more accurately, columnar spacers are formed on the counter substrate and the gap is controlled by the columnar spacers.
However, use of the columnar spacer additionally raises a new problem. JP-2000-122071-A, JP-2001-33790-A, and JP-2002-229040-A describe the following. When the columnar spacer is formed on the TFT substrate, a reservoir of the alignment film is formed at the periphery of the columnar spacer and the thickness of the alignment film is increased therein. To prevent such increase in the thickness, a concave portion is formed at the top end of the columnar spacer to retain the alignment film in the concave portion thereby preventing increase in the thickness of the alignment film at the periphery of the columnar spacer.
JP-2009-255529-A describes the configuration in which grooves are formed, for example, of a concentric shape at the top end of the columnar spacer and the liquid alignment film is accumulated in the grooves to prevent scraping of the alignment film after drying. Further, the configuration is adapted to ensure the degree of freedom of the size of a pedestal disposed in facing relation to the columnar spacer.
JP-2007-94372-A describes the configuration in which grooves are formed at the surface of a pedestal disposed in facing relation to a columnar spacer and the area of contact between the columnar spacer and the pedestal is adjusted to shorten the recovery time after the substrate has been pressed from the outside.